Electrolytic production of metals



Dec; 29j 1925. 1,567,791

E. DUHME ELECTROLYTIG PRODUCTION OF METALS Filedl Nov, l, 1924 gef-werde# Inode lfatented 29, l9259 nutren stares @FFlCG vElill'lh DUHME, 0F BERLIN-CHRLTTENBURG, GERMANY, SSIGNOR LTO SIEMENS &

EALSKE, AKTIENGESELLSCHAFT, F SIEMENSSTADT, NEAR BERLIN, A CQTRPOIR- irren or GERMANY.

ELECTROLYTC PRODUCTEON 0F METALS.

Application filed November l, i924. Serial No. 747,366.

Electrolytic Production of Metals, of which" the 'following' is a specification.

My invention relates to improvements in the electrolytic production of metals.

The hitherto employed processes for electrolytically producing metals show the drawback that the impurities ci the anode material are deposited or precipitated on the cathode together with the metal so that the product of the process is a metal which contains a certain amount of impurities.

The ohject 'of my invention is a process and apparatus in theY impurities of the anode material arev ept away from the 2 9 cathode'so that the 'product obtained is a redegrees o purity or refinement can loe oh` Aas ned or almost pure metal.

The invention is hasedon the recognition that hy electrolytically depositing metal on a plurality of cathodes, depositsfoi dierent tained if the individual cathodes 'are dil ierently disposed relatively to the anode either electrically or with regard to distance. The di'erence in the composition ot the deposits obtained on the several cath odes resides in the fact that the transition ol the metal from the anode to the cathode is a purely electrical process,`whereas the `transition of the impurities from the anode to the cathode is an ical process.

"lfhus,l according to the present invention, even if only two cathodes are employed, ci which for instance, one is disposed at a smaller distance from the anode 4than the other, deposits of different degrees of purity may he obtained on these cathodes. lt, is

true that in such cases a considerable per` centage of the metal to be puried will he deposited at the nearer cathode, but a hy far greater percentage of impurities will likewise be deposited on this nearer cathode. l shall designate in the following description the cathode on which the greater percentage of im urities are deposited, as auxiliary' catho e and the other cathode on whichthe alpmcst exclusively chem-V,

refined desired metal is deposited, the main cathode. i The eec't referred to hereinbefore results from the diffusion of the impurities contained in the metals through the electrolyte,

and thus the concentration of the impurities.

will be the smaller, the greater the distance is between the cathode and the anode. sides the impurities contained in the metals to loe rened are largely of xa. nature, electrically, such that they have a greater tendency to deposit than the metals to lie relined, and therefore they will deposit to a very large extent at the nearer cathode, i. e.,

the auxiliary cathode. By thus repeating the process just described, the initially small dierence in purity of the deposited metal at the two cathodes may gradually he increased.

This dilference in composition o the' deposits at different distances of the cathodes from the anode can he considerably .increased hy making the auxiliary cathode of smaller area than the -more remote or. main cathode. Thislwill result in a greater portion ci the desired metal traveling tothe main cathode, while at the same time the difference in surface between the two cathodes has no eect with regard to the deposition on?. impurities. l l

lt is desirable to deposit on the auxiliary cathode, whose deposits largely are to consist of impurities, only so much or the olesiredmetal as is necessary for binding the impurities. For this purpose, according to 1 thode aside from the impurities only as p much metal as is necessary for binding the impurities, the direct current flowing he tween the anode and the auxiliary cathodeaside from the alternating current flowing therebetween-is made correspondingly smaller in intensity. This decrease in direct current may be attained for instance by inserting a resistance between the auxiliary cathode and the negative pole of the direct current source. Thus an lunsymmetrical alternating current, as it were, iiows between the anode and the auxiliary cathode. The eii'ect obtained thereby .is essentially as follows:

The alternating current which Hows between the anode and the auxiliarycathode prevents .a deposit of the desired metal on the auxiliary cathode. However, since, aside from the alternating-current also direct current of small intensity flows between the auxiliary cathode and the anode, a small percentage of the desired metal is deposited on the auxiliary cathode by means of this small direct current. This small amount of metal deposit is suicient to bind the impurities which diffuse through the electrolyte and which are deposited on the auxiliary cathode so that only a very small percentage of these impurities travels to the main cathode in whose vicinity the concentration of the impurities in the electrolyte is very much smaller than in the vicinity of the auxiliary cathode. The strong direct current which ows between the anode'and the main cathode now causes the deposition of the metal on the main cathode except the small portion of metal which remains on the auxiliary cathode on account of the alternating currentilowing.

In the drawing aiiixed to this specification and forming part thereof an .apparatus is illustrated which is adapted to carry out the above` described process for obtainingrelined metals and more particularly for obtaining iron free from phosphorus.

Referring to this drawing, 1 is a vessel or tank containing the electrolyte, 2 a cylindrical anode, 3 the main cathode and. 4 the auxiliary cathode. This auxiliary cathode 4 is cylindrical and perforated. In the interior of the auxiliary cathode 4 is located the main cathode 3. The anode 2 and the main cathode 3 are directly connected with the ,source of continuous current 5, the auxiliary cathode 4 being connected with the negative pole of `the source of continuous current across a resistance 6. Between anode and auxiliary cathode 4 there is, furthermore, connected a source 7 of alternating current which gives satisfactory results at the usual frequency of, for instance, 40 to 50 cycles.

' The action of this improved process is probably based on the fact that those phases of the alternating current during which the electrode 4 becomes anode and the electrode 2 cathode increase the concentration of the impurities, for instance, the phosphorus comhina-tions, because under the infiuence of electrolysis these combinations travel to the anode for the time being. The subsequently reversed direction of the current brought, about by the alternation of the current makes the electrode4 into a cathode. The'hydrogen in its nascent state generated at the auxiliary cathode besides the iron deposit reduces the previously, accumulated phosphorus combina-tions. The liberated phosphorus combines at the auxiliary cathode with the iron into iron phosphide. The iron at the anode 2 serving for the production of the solution passes to the main cathode 3 where it is deposited in almost pure state.

Experiments have shown that the contents of phosphorus of the iron deposited on 'the main cathodemay by means of the improved process 4be reduced to less than one thousandth of the phosphorus previously c ontained in the anode.

What Iclaim as my invention is l. A process for electrolytically depositing metals substantially free from impurities'on a cathode, consisting in maintaining an auxiliary cathode nearer the anode than the main cathode on which latter the desired pure metal is to be deposited and in supplying a suitable current to said auxiliary cathode and said anode, causing a comparatively small but desired metal depositl on the auxiliary cathode, whereby', due to larger concentration of the impurities near the anode, they are deposited on the auxiliary cathode to a greater' extent than on the more remote main cathode.

2. A process for electrolytically depositing metals substantially free from impurities on a cathode, consisting in maintaining an auxiliary cathode nearer the anode and of smaller area than the main cathode on which latter the desired pure metal is to be de# positedV and in supplying a suitable current to said auxiliary cathode and said anode, whereby due to the larger main cathode area a greater portion of the desired metal is deposited on the main cathode.

3. 'A process for electrolytically depositling metals substantially free from impurities on a cathode, consisting in maintaining an auxiliary cathode nearer the anode than the main cathode on which latter the desired pure metal is to be deposited, and in supplying an unsymmetrical alternating current to said auxiliary cathode and said anode, cans! ing a comparatively small but "desired metal deposit on the auxiliary cathode, sulicient to bind the impurities deposited thereon, Whereby'due to larger concentration of the impurities near the anode, they are deposited on the auxiliary cathode to a greater extent p than on the more remote main cathode.

4. A process for electrolytically depositing metals substantially free from impurities on a cathode, consisting in maintaining .en auxiliary cathode nearer the anode than the main cathode on which atter the desired pure metal is to be deposited and in supplying direct current of suitable voltage to `said anode and main cathode, and in supplying te said anode and aluxiliary cathode alter# meting current of sutabie voitege and' also direct 'current of lower veitage than the 

